Apparatus for coating metal



y 23, 1939- B. RfsHovER APPARATUS FOR COATING METAL Filed July 26, 19324 Sheets-Sheet 1 gj iil'p Q l May 23, 1939. B. R. SHOVER APPARATUS FORCOATING METAL Filed July 26, 1932 4 Sheets-Sheet 2 INVE TOR e. fi w y1939- B. R. SHOVER 2,159,297

APPARATUS FOR COATING METAL Filed July 26, 1952 4 Sheets-Sheet 3INVENTOR Patented May 23, 1939 UNITED STATES PATENT OFFICE APPARATUS FORCOATING METAL Application June 26, 1932, Serial No. 624,753

3 Claims.

This invention relates to apparatus for coating metal. It is describedparticularly herein as applied to coating strip metal, although it is ofgeneral utility for coating sheets, plates, wires and other shapes. Inthe description and claims, the term strip is used as a term of generaldefinition to include articles in general and is not intended to berestricted to articles of any particular width or length. ln Formanyyears tin plate and galvanized sheets have been made by passing apreviously cleaned sheet through molten tin or zinc. The base metal tobe coated has been carried through the coating bath by rollers and thetop of the bath has been covered with a flux. The molten coating metalbecomes oxidized to a certain extent in spite of the flux. the oxideformed contaminating the bath. The bath is further contaminated by adross which is formed by alloyage of the base metal with the coatingmetal. The dross and oxides sometimes adhere to the strip, causing thecoating to be defective. The foreign particles formed by oxidation ofthe bath or alloyage of the strip with the coating metal have a tendencyto collect at the entrance side of the rollers used in conveying thestrip through the bath, and after a time these impurities pass throughthe rolls and collect on the strip, thereby marring the coating.

The disadvantages inherent in the coating methods heretofore employedare eliminated or decreased by the present invention. In the presentinvention, the coating bath and strip are protected from oxidation bysupplying a protective gas such as hydrogen, nitrogen, cracked ammoniaor natural gas to the furnace in which the coating metal is contained.The strip is preheated before the coating metal is applied thereto so asto insure the coating metal will take.

The coating metal is applied to the strip in one or more streams and theexcess of coating metal, after having been applied to the strip, iscollected and again pumped so as to form streams of coating metal whichare used to coat subsequent portions of the strip. Other features of theinvention are pointed out more particularly hereinafter.

In the accompanying drawings, which illustrate several embodiments of myinvention:

Figure 1 is a longitudinal vertical section through the apparatus;

Figure 2 is a transverse vertical section on the line IL-II of Figure 1;

'5 Figure 3 is a partial plan view and partial horizlontal section onthe line III-III of Figure Figure 4 is a vertical section taken on theline IV-IV of Figure 3;

Figure 5 is a longitudinal vertical section of a 5 modified form of theinvention in which electric resistance heating units are used forpreheating the strip;

Figure 6 is an enlarged section on the line VI-VI of Figure 5,'and 10Figure '7 is a view similar to Figure 6 but illustrating the preheatingof the strip by means of a burner instead of electric resistance heatingunits.

Referring more particularly to the accompanyl5 ing drawings, andespecially to Figures 1 through 4, the coating apparatus, which isindicated generally by the reference numeral 2, has a pre heatingchamber 3 adjacent its entrance end. The chamber is heated by burners 4and the 29 products of combustion pass upwardly around a muflle 5arranged in the preheating chamber 3. The combustion gases then passthrough a chamber 6 formed between metal plates 1 and 8 and escapethrough a stack 9 located adjacent 5 the exit end of the apparatus. Ifdesired, a portion of the combustion gases may be passed directly to astack 9' located near the entrance end of the apparatus, the stack beingcontrolled by a damper 917. A strip II) which is to be coated 30 isconveyed into the furnace by rollers ll adjacent the entrance end of thefurnace, through a gas seal at l2, through the slot l2 in the end of themuffle 5 and is guided by rollers l3, l4 and i5 through a flux pot 16.From the flux pot, 35 the strip passes through the molten coating metalin a container or pot I1 and is then fed upwardly through the coatingchamber l9 and the cooling chamber 20. Pinch rolls 2| are used forpulling the strip through the coating apparatus. As the 40 strip passesthrough the coating chamber 19, streams of coating metal are sprayedagainst it by nozzles 22 arranged on opposite sides of the strip. Theforcible impacting of the molten coating metal against the strip is forthe purpose 45 of causing good adherence and a certain amount ofalloyage of the coating metal and strip. These nozzles may be arrangedto deliver the molten metal at any angle desired. The coating metalflows down over the strip and into the pot ll, from which it is returnedto the nozzles by means of a pump 25 and pipe 26.

The dross formed by alloyage of the strip with the coating metal is ofonly slightly greater specific gravity than the coating metal, and any5' settling of the dross. In order to prevent agitation of the bath bythe coating metal dripping from the sheet, a baiile 2l is providedadjacent the top of the bath. The baille is shaped so as to slope at aslight angle with the surface of the bath, and in this way,any coatingmetal which may drop oil of the sheet is returned to the bath withoutagitating it unduly. The suction of the pump is preferably located'onlyslightly below the surface of the bath so that it will return to thenozzles 22 only pure coating metal and not that which is contaminated bythe dross. Since the bath is substantially free from agitation due tothe omission of any feed rolls therein, the dross settles to the bottomof the tank and may be withdrawn through a pipe 28.

In the usual type of coating apparatus, the coating pot is heated fromthe bottom or sides. This causes convection currents to be set up in thebath which prevent rapid settling of the dross. The dross is picked upby the sheet passing through the bath and may form an imperfect coatingthereon. Since, according to this invention, the surface of the bath andthe strip which is to be coated are protected from oxidation by flowinga protective gas through the coating apparatus, no flux is needed on thetop of the bath, and the bath may be heated from the top rather thanfrom the bottom or sides. The heating of the bath surface rather thanthe bottom or sides thereof decreases the formation of convectioncurrents which would agitate the bath and interfere with the settling ofdross. In

this invention, the coating metal in the pot Il may be heated at thestart of the operation in order to melt it by means of burners 29, butthereafter during the process these burners are not used, the necessaryheat for maintaining the bath molten being provided by other heatingmeans arranged adjacent the top of the bath. In Figure 1, I have shownelectric resistance heating elements for this purpose, but burners maybe used if desired. The strip itself may also be used to supply heat tothe bath metal, the strip being preheated by the heating elements illand the burners 4 to a temperature higher than the bath prior to theentrance of the strip into the bath.

In order to further guard against agitation of,

the bath metal, a baflle 3! is secured to the side of the pot I l andextends toward the center of the pot a suflicient distance to preventeddy currents being set up in the bath adjacent the inlet of the pump.

The gas which is used for protecting the surface of the coating metaland the strip from oxidation is supplied through a pipe 32 locatedadjacent the upper end of the cooling stack 20. The cooling stack andthe strip and protective gas flowing therethrough are cooled by means ofa cooling coil 33 which may be supplied with water or other coolingfluid through an entrance pipe 34 and anexit pipe 35. The protectivegas, after flowing downwardly through the cooling chamber 20, passesthrough the coating chamber I9, then over the top of the pots I! and I6and into the muflle 5. It may be conducted to the preheating chamber 3by a pipe 36, where it may be burned to supplement the heat supplied bythe burners l.

The feed rolls Ii are driven from a motor through gearing 4| and therolls ii are driven from a motor 42 through gearing l3. Pinch rolls 2|are driven by motor 44. The top of the coat- I there is shown a singleconveying 2,159,297 agitation of the coating bath tends to prevent ingapparatus adjacent the flux pot l6 is provided with a cover 45 having aseal 46 so that the cover may be removed in order to gain access to theinterior of the apparatus. A window 41,

which may be closed by a plug 48, is provided adjacent the lower end ofthe coating chamber I9 for gaining access to the nozzles '22.

The pump 25 which supplies coating metal to the nozzles 22 is driven bya motor 50. The motor is supported on a removable cover 5| forming apart of the top of the coating apparatus over the coating pot IT. Thecover 5| is preferably of such size that when it is removed the motor50,

pump shaft 52, pump 25, pipe 26 and nozzles 22 may be removed as a unitfrom the apparatus.

From time to time it is necessary to supply the coating pot with metalto compensate for that used in coating the strip. This is ordinarilydone by dumping additional coating metal into the open bath. In thepresent invention, the oxidation of the bath is reduced when addingcoating metal thereto by providing the pot with a conduit whichcommunicates at one end with the bath below the surface thereof and hasits other end lying outside of the apparatus. As shown in Figures 3 and4, the pot I1 is provided at one end with an extension forming a conduitor trough 56 having its lower end 51 communicating with the metal in thepot below the surface thereof. The upper end of the trough lies outsideof the coating apparatus and is provided with a cover 58. By means ofthe feed trough, additional coating metal may be supplied to the potwithout exposing the main portion of the bath metal to oxidation.Oxidation of the small portion 59 of the bath surface which lies in thetrough may be prevented by supplying protective gas to the space abovethe bath level through a pipe 60 controlled by a valve 8|. As this spaceis small, it requires only a very small amount of gas to preventoxidation of the metal. The valve 6| has a handle 62 which is positionedin the path of movement of the cover 58 so that as the cover is movedinto its dotted line position in order to feed additional metal to thebath, it closes the valve, thereby preventing waste of the protectivegas during the time that the cover is in open position. A spring 63opens the valve when the feed trough is closed by the cover.

In Figure 5 there is shown a modified type of apparatus which isgenerally similar to that described heretofore, but which is heatedentirely by electric resistance elements instead of by the combustion offuel as in the preheating chamber 3 shown in Figure 1. In Figure 5,parts corresponding to those already described have been indicated bythe same reference numerals with an 41" aflixed thereto. The stripbefore entering the flux pot Ito and the coating pot Ila is preheated bypassing in contact with pairs of rollers ill which are heated byelectric resistance heating elements H mounted in their interiors, asshown in Figure 6. Current is supplied to the heating elements by meansof collector rings 12 and lead wires 13. In this construction, the stripis preheated by conduction due to the direct contact of the heated rollswith the strip. This is a more efficient mannerof transmitting heat thanby radiation described in the other embodiment. Instead of passingbetween pairs of rolls, the

and instead of using electric resistance heating units in the interiorsof the rolls, the roll interiors may be heated by burners. In Figure '7,

roll 14 over which the strip 10a is conveyed. The interior of the rollis heated by a burner which may be supplied with fuel from any desiredsource.

In the embodiment shown in Figure 5, the chamber 6 shown in Figure 1 iseliminated and the coating chamber [9a, instead of having itstemperature maintained by products of combustion, is heated by electricresistors 16 and the coating chamber is surrounded by a layer 11 ofinsulating material.

In Figure 1, the strip passes through the bath of coating metal in thepot l1 before the streams of coating metal are applied thereto in thecoating chamber l9. In Figure 5, the strip passes directly from therolls I5a to the nozzles 22a without passing through the bath metal inthe pot I121. The strip may or may not pass through the metal in thepot, as desired, whether the preheating be done by electricity orproducts of combustion. In Figure 5, the coating is accomplishedentirely by the streams of coating metal supplied by the nozzles 2211,whereas in Figure 1, the coating is supplemented by the strip firstpassing through the bath. In those cases where the/strip passes throughthe bath, it is preferred to maintain the strip adjacent the top of thebath in. order to prevent an undue amount of agitation of the bath,which agitation would decrease settling of the dross. If desired, a pairof conveying rolls may be placed in the coating chamber l9 or [9a to aidin conveying and guiding the strip through the chamber. Although it ispreferred to locate the pump 25 in the coating pot, it may be placedoutside of the pot, but in communication with the coating metal.

In some cases, it may be found desirable to apply the flux to the stripin stream form, as has been described in connection with the applicationof coating metal to the strip, instead of passing the strip through theflux bath. Furthermore, in some cases, the flux may be entirelyeliminated since the strip and the bath are protected against oxidationdue to the use of the protective gas. If desired, the strip, afterhaving been coated and the coating allowed to solidify, may be suppliedwith an additional coating by conveying it through a second coatingchamber which is supplied with protective gas and which has a second setof nozzles for supplying the second coating of metal to the alreadycoated strip.

Although the coating chambers 19 and 19a have been shown and describedas provided with means for heating them either by combustion gases orelectric resistors, they may be simply heat insulated portions of thestack. Also, cooling coils need not be employed in the cooling chambers20 and 20a so long as the walls of the cooling chambers have good heatconducting properties.

I have illustrated and described several embodiments of my invention. Itis to be understood, however, that the invention may be otherwiseembodied or practiced within the scope of the following claims.

I claim:

1. Apparatus for coating strip metal, comprising a chamber sealed fromthe atmosphere, means for conveying the strip through the chamber, meansfor heating the strip while passing through the chamber, a container fora bath of molten coating metal in the chamber, means for supplying astream of molten coating metal from the container to the strip outsidethe bath and returning the excess coating metal to the container, meansfor maintaining that portion of the chamber adjacent the coating meansat a temperature at least as high as the melting point of the coatingmetal, a baffle in the container between the surface of the coatingmetal bath and the point where the coating metal is applied to thestrip, said baflie decreasing agitation of the bath by excess coatingmetal returned thereto from the strip, and means for supplyingprotective gas to the chamber to prevent oxidation of the strip andcoating metal.

2. Apparatus for coating strip metal, comprising a chamber sealed fromthe atmosphere, means for conveying the strip through the chamber, meansfor heating the strip while passing through the chamber, a container fora bath of molten coating metal in the chamber. a pump in the containerfor supplying a stream of molten coating metal to the strip outside thebath and returning it to the container, a baflie in the coating metal inthe container below the pump inlet for decreasing agitation of thebottom of the bath by the pump, and means for supplying protective gasto the chamber to prevent oxidation of the strip and coating metal.

3. In apparatus for coating metal, a container for coating metal, a feedconduit for metal having one end communicating with the interior oi! thecontainer below the bath level and the other end extending outside ofthe container, 9. cover for the conduit, and means for supplyingprotective gas to the conduit.

BARTON R. SHOVIR.

